Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions				3 Months Ended
	Apr. 26, 2017	Apr. 24, 2017	Feb. 14, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Apr. 25, 2017	Apr. 19, 2017	Apr. 05, 2017
Subsequent Event [Line Items]
Pre-tax gain on sale of common stock			$ 351,000,000
Interest expense					$ 115,000,000	$ 121,000,000
Scenario, Forecast [Member]
Subsequent Event [Line Items]
Pre-tax gain on sale of common stock				$ 167,000,000
Minimum [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Interest expense				50,000,000
Maximum [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Interest expense				$ 60,000,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Aggregate principal amount								$ 795,000,000
Amount of notes purchased		$ 295,000,000
Senior notes purchased for cash	$ 77,000,000	$ 320,000,000
Remaining amount of notes agreed to sell by purchaser							$ 500,000,000
Senior notes purchased for shares	12,958,767
Tender offers expiration date	May 02, 2017
Debt instrument conversion price	$ 35.91
Subsequent Event [Member] | 2018 Notes [Member]
Subsequent Event [Line Items]
Maximum purchase of aggregate principal amount									$ 1,000,000,000